This invention relates to optoelectronic devices and more particularly to devices comprising an arrangement to direct light. The invention also relates to a method of forming a light directing arrangement for an optoelectronic device.
One known type of light emitting device comprises a junction in a body of silicon and which junction is configured to be driven into avalanche or field emission breakdown mode thereby to emit light. A problem associated with these devices is that the critical angle of internal reflection at the silicon-oxide-air interface is determined by the refractive indexes of the materials. For silicon and air, the critical angle is only about 15.3° and taking into account the solid angles of emission, it means that only about 1.8% of the light generated by the device will leave the surface. A large proportion of this light leaves the surface of the body substantially parallel to the surface and therefore it is difficult to effectively couple this light into an input of a spaced optical fibre.
It is also known that the speed with which semiconductor pn junction diode optical detectors operate, is a function of the built-in junction capacitance. By reducing the size of the detecting pn junction, the built-in pn junction capacitance may be reduced, and the detecting diode device may operate at a higher switching frequency. However, at the same time, the sensitive area of the detector is also reduced, resulting in a smaller optical signal being detected, which is not desirable.